The present invention relates to pressure vents for fuel storage tanks and, in particular, to a pressure valve which utilizes a liquid column to respond to both high pressure and low pressure situations in a fuel storage tank.
Conventional pressure and vacuum vents utilize springs, diaphragms, or weights to open and close the valves at a predetermined pressure or vacuum levels. For example, a conventional vent may utilize a number of springs or weights to open the valve at a positive pressure level equivalent to 3.0 inches of water, and at a negative pressure level (vacuum) equivalent to 8.0 inches of water. However, a slight change in the weight or strength of the spring will result in the conventional valve opening either above or below the desired pressure or vacuum setting.
Further, due to the designs, conventional pressure and vacuum vents utilizing springs, weights, or diaphragms have a greatly diminished amount of force holding the valve in the closed position as the pressure or vacuum approaches the predetermined opening levels. As the amount of force holding the valve closed decreases, leakage may occur through the valve. Such designs of particularly susceptible to leakage if dirt or contaminates have collected on the valve seat, preventing the complete closure or sealing thereof.
Accordingly, there is a need in the fuel tank industry for a simple combination pressure and vacuum valve which opens at predetermined high and low pressure levels, and which maintains a consistent seal for intermediate pressures.